1. Field of the Invention
The present invention relates to a fuel transporting tube and particularly to such a tube which has a laminated structure including a plurality of layers, which exhibits an excellent resistance to permeation of fuels, e.g., not only gasoline but also alcohol-blended gasoline, an excellent detergent resistance, and an excellent hydrolysis-deterioration resistance, and exhibits an excellent resistance to interlayer separation when being used in a high-temperature atmosphere, and which is particularly suitable for use in a fuel-transporting piping system of an automotive vehicle.
2. Related Art Statement
A fuel-transporting piping system of an automotive vehicle includes a feed tube, a return tube, an evaporator hose, a breather hose, a filler hose, an ORVR-tube, or the like. Conventionally, various sorts of metallic, rubber, or resinous tubes or hoses have been used in the piping system. Recently, resinous tubes are widely used in consideration of cost performance, in particular. Meanwhile, national regulations regarding fuel evaporative emission have been stricter and stricter in consideration of environmental problems. That is, it is strongly desired to minimize the amount of fuel that permeates through the tubes and transpires into the atmosphere.
In United States of America, alcohol-blended gasoline is commercially used as a fuel of automotive vehicles. Generally, the amount of alcohol-blended gasoline that permeates out through a resinous or rubber tube is much more than that of non-blended gasoline that does not contain alcohol. Thus, it is desired to develop a tube which has an excellent resistance to permeation of not only non-blended gasoline but also alcohol-blended gasoline.
Various proposals have been made in the above-indicated background. For example, Japanese Patent Document TOKU-KAI-HEI No. 4(1992)-224384 discloses a fuel transporting tube including, as its fuel barrier layer, an innermost layer which is formed of a polyester resin such as polyethylene terephthalate or polybutylene terephthalate, and U.S. Pat. No. 5,425,817 discloses a multi-layer plastic tube including an innermost layer and an outermost layer each of which is formed of a polyamide, and including, as a low-permeation layer, an intermediate layer which is formed of a linear-crystalline polyester such as polyethylene terephthalate or polybutylene terephthalate. In addition, Japanese Pat. Document TOKU-KAI-HEI No. 6(1994)-23930 discloses a multi-layer polymer hose or pipe including an innermost layer and an outermost layer each of which is formed of a polyamide, and including, as a low-permeation layer, an intermediate layer which is formed of a polyester resin such as polyethylene terephthalate, polybutylene terephthalate, or polyethylene naphthalate, and European Patent Application No. 0686797 A1 discloses a multi-layer plastic tube including, as a low-permeation layer, an innermost layer which is formed of a thermoplastic polyester such as polyethylene terephthalate or polybutylene terephthalate.
However, even the above-indicated multi-layer or laminated tubes that are claimed to be resistant to permeation of alcohol-blended gasoline, do not satisfactorily meet the currently desired, very strict requirement regarding the resistance to permeation of alcohol-blended gasoline, even if those resins disclosed in the prior documents may be selected anyway.
Out of the above-indicated tubes, ones whose innermost layer is formed of polyethylene terephthalate or polybutylene terephthalate are deteriorated, during a long period of use, because of an amine detergent that is usually added to a fuel for the purpose of removing stains of an intake valve. That is, those tubes do not exhibit a sufficiently high detergent resistance. In addition, tubes whose innermost layer is formed of one of the resins disclosed in the prior documents do not exhibit a sufficiently high resistance to hydrolysis of innermost layer. More specifically described, the innermost layer may be hydrolyzed because of water contained in the fuel, or moisture present in the atmosphere. Therefore, those tubes do not exhibit a sufficiently high reliability when being used as fuel transporting tubes for a long period in a high-temperature atmosphere.
Moreover, in the case where the low-permeation layers are used as not the respective innermost layers of tubes but the respective intermediate layers thereof, the intermediate layers may peel or separate from respective layers- provided radially inwardly of the intermediate layers, in particular when being used in a high-temperature atmosphere. Thus, the tubes including, as their intermediate layers, the low-permeation layers do not exhibit a sufficiently high reliability.
By the way, Japanese Patent Document TOKU-KAI-HEI No. 7(1995)-96564 discloses a fuel transporting tube which is claimed to be able to be used as a low-permeation or anti-permeation layer against alcohol-blended gasoline, and which includes, as an anti-permeation layer, an intermediate layer formed of a polyalkylene naphthalate resin, such as polybutylene naphthalate, that exhibits a higher permeation resistance than a polyester resin, such as polybutylene terephthalate, and additionally includes an innermost layer which is formed of a fluororesin or a polyamide. Since the fuel transporting tube has a laminated structure including the above-indicated resinous innermost layer, the anti-permeation intermediate layer may separate from the innermost layer located inside the intermediate layer, because of the fuel which permeates out through the innermost layer, though an adhesive layer is provided between the intermediate layer and the innermost layer. Thus, the tube does not exhibit a sufficiently high reliability.
In particular, since the innermost layer formed of fluororesin or polyamide resin is provided inside the low-permeation or anti-permeation intermediate layer, the tube has an increased overall wall thickness, which leads to limiting the thickness of the intermediate layer, thereby limiting the anti-permeation function of the same. In addition, in the case where the innermost layer is formed of polyamide resin, the innermost layer may be less resistant to sour gasoline than the polybutylene naphthalate resin. Meanwhile, in the case where the innermost layer is formed of fluororesin, the innermost layer may exhibit a low detergent resistance, and may exhibit a low sealing characteristic because the fluororesin has a low friction coefficient and is highly slidable relative to a coupling or a metallic member being inserted into an open end of the tube.
It is therefore an object of the present invention to provide a fuel transporting tube which exhibits an excellent resistance to permeation of not only gasoline but also alcohol-blended gasoline, an excellent detergent resistance, and an excellent hydrolysis resistance, and exhibit an excellent resistance to interlayer separation when being used in a high-temperature atmosphere.
The present invention provides a fuel transporting tube which has one or more of the technical features that are described below in respective paragraphs given parenthesized sequential numbers (1) to (17). Any feature which includes another feature shall do so by referring, at the beginning, to the parenthesized sequential number given to that feature. Thus, two or more of the following features may be combined, if appropriate. Each feature may be accompanied by a supplemental explanation, as needed. However, the following features and the appropriate combinations thereof are just examples to which the present invention is by no means limited.
(1) According to a first feature of the present invention, there is provided a fuel transporting tube comprising an inner layer which contacts a fuel being transported and which is formed of a polybutylene naphthalate resin; an outer layer which is provided radially outwardly of the inner layer and which is formed of a polyamide resin or a polyolefin resin; and an intermediate layer which is provided between the inner layer and the outer layer and which is formed of a resin to adhere the inner and outer layers to each other.
In the present fuel transporting tube, the inner layer that contacts the fuel being transported by the tube is formed of the polybutylene naphthalate resin. Therefore, the present tube exhibits an excellent resistance to permeation of fuels, e.g., not only common gasoline but also alcohol-blended gasoline. Even in the case where an amine detergent is added to the fuel, the present tube exhibits an excellent resistance to deterioration due to the detergent. Moreover, the present tube exhibits an excellent resistance to deterioration due to hydrolysis. Thus, the present tube exhibits a high reliability in a long-time use. Furthermore, the present tube exhibits an excellent resistance to interlayer separation when being used in a high-temperature atmosphere. The present tube does not need any additional layers inside the inner layer formed of the polybutylene naphthalate resin. Therefore, the thickness of the inner layer formed of the polybutylene naphthalate resin can be increased by the thickness of the unnecessary layer or layers, so as to improve the resistance to permeation of alcohol-blended gasoline. The polybutylene naphthalate resin exhibits a higher resistance to sour gasoline than polyamide resin, and is free of a problem with fluororesin that an innermost layer formed of the fluororesin exhibits a low sealing characteristic because a coupling or a metallic member may slide relative to the tube when being inserted in an open end of the tube.
(2) According to a second feature of the present invention that includes the first feature (1), the inner layer comprises a conductive layer which is formed of a composition comprising the polybutylene naphthalate resin and an electrically conductive material. Since the inner layer of the present tube that contacts the fuel being transported is electrically conductive, the present tube is advantageously used as a tube, e.g., a filler tube, a feed tube, or a return tube, that should be prevented from producing sparks due to discharging of electric charge.
(3) According to a third feature of the present invention that includes the first feature (1), the inner layer comprises a conductive inside layer which contacts the fuel and which is formed of a composition comprising the polybutylene naphthalate resin and an electrically conductive material; and a non-conductive outside layer which is provided radially outwardly of the inside layer and which is formed of the polybutylene naphthalate resin and does not include any electrically conductive materials. The present tube enjoys the same advantage as that of the tube according to the second feature (2).
(4) According to a fourth feature of the present invention that includes any one of the first to third features (1) to (3), the intermediate layer is formed of at least one resin selected from the group consisting of a thermoplastic polyether urethane, a thermoplastic polyester urethane, a thermoplastic polyether amide elastomer, a thermoplastic polyester amide elastomer, a thermoplastic polyester elastomer, a mixture of a thermoplastic polyester elastomer and a polyamide, a mixture of a polyester and a polyamide, a maleic anhydride-modified polyolefin, an acrylic acid-modified polyolefin, an epoxy-modified polyolefin, a maleic anhydride-olefin copolymer, and an alkylacrylate-olefin copolymer. In the present tube, the intermediate layer advantageously connects the inner and outer layers to each other and thereby unifies the two layers.
(5) According to a fifth feature of the present invention that includes any one of the first to fourth features (1) to (4), the polybutylene naphthalate resin comprises a block-copolymer which includes, as a hard segment thereof, a polybutylene naphthalate unit, and includes, as a soft segment thereof, a polyether unit or a polyester unit. Since the inner layer of the present tube is formed of the block-copolymer as the polybutylene naphthalate resin, the softness or flexibility of the inner layer is improved. In addition, the melting point of the polybutylene naphthalate resin is lowered down to a temperature near a temperature around which the outer layer is formed of the polyamide or polyolefin resin. Thus, the inner and outer layers can be more advantageously formed by concurrent or simultaneous extrusion.
(6) According to a sixth feature of the present invention that includes any one of the first to fifth features (1) to (5), at least a portion of the tube has a corrugated shape which includes at least one annular ridge and at least one annular groove which are alternate with each other and each of which extends parallel to a plane perpendicular to a lengthwise direction of the tube. The present tube as a whole can enjoy an improved flexibility, even if the inner layer formed of the polybutylene terephthalate resin may have a great thickness. Thus, the present tube enjoys not only an improved permeation resistance but also an improved ease of being handled and/or being assembled with other members.
(7) According to a seventh feature of the present invention that includes any one of the first to fourth and sixth features (1) to (4) and (6), the polybutylene naphthalate resin comprises a condensation polymerization product of a naphthalenedicarboxylic acid or its derivative capable of producing an ester, and tetramethylene glycol.
(8) According to an eighth feature of the present invention that includes the seventh feature (7), the naphthalenedicarboxylic acid is selected from the group consisting of 1,4-naphthalenedicarboxylic acid,
1,5-naphthalenedicarboxylic acid,
2,6-naphthalenedicarboxylic acid, and
2,7-naphthalenedicarboxylic acid.
(9) According to a ninth feature of the present invention that includes the fifth or sixth feature (5) or (6), the polyether unit comprises a segment consisting of a naphthalenedicarboxylic acid or terephthalic acid and HO(CH2CH2O)nH or HO(CH2CH2CH2CH2O)nH (n is an integer).
(10) According to a tenth feature of the present invention that includes any one of the fifth, sixth and ninth features (5), (6) and (9), the polyester unit comprises a unit selected from the group consisting of polycaprolactone, polyenantholactone, and polycaprylolactone.
(11) According to an eleventh feature of the present invention that includes any one of the fifth, sixth, ninth and tenth features (5), (6), (9) and (10), the block-copolymer includes not more than 40 parts by weight of the soft segment and not less than 60 parts by weight of the hard segment.
(12) According to a twelfth feature of the present invention that includes any one of the second to eleventh features (2) to (11), the composition comprises 3 to 30 parts by weight of the electrically conductive material per 100 parts by weight of the polybutylene naphthalate resin.
(13) According to a thirteenth feature of the present invention that includes any one of the first to twelfth features (1) to (12), the polyamide resin is selected from the group consisting of nylon 6, nylon 66, nylon 11, nylon 12, nylon 610, and nylon 612.
(14) According to a fourteenth feature of the present invention that includes any one of the first to thirteenth features (1) to (13), the polyolefin resin is selected from the group consisting of a homopolymer and a copolymer of an olefin monomer selected from the group consisting of ethylene, propylene, butene, hexene, and octene, and a thermoplastic elastomer including, as a main component thereof, the homopolymer or the copolymer.
(15) According to a fifteenth feature of the present invention that includes any one of the first to fourteenth features (1) to (14), an outer diameter of the tube falls within a range of 8 to 50 mm, and a sum of respective thicknesses of the inner layer, the intermediate layer, and the outer layer falls within a range of 0.8 to 2.0 mm.
(16) According to a sixteenth feature of the present invention that includes any one of the first to fifteenth features (1) to (15), a thickness of the inner layer falls within a range of 0.04 to 1.0 mm, a thickness of the intermediate layer falls within a range of 0.02 to 0.5 mm, and a thickness of the outer layer falls within a range of 0.4 to 1.40 mm.
(17) According to a seventeenth feature of the present invention that includes any one of the third to sixteenth features (3) to (16), a thickness of the inside layer of the inner layer falls within a range of 5 to 50% of a sum of respective thicknesses of the inside layer and the outside layer of the inner layer.